The present invention relates to a burner, being installed on a wall surface of a boiler furnace and used for burning fuels such as pulverized coal, fuel oil, heavy oil, etc.
The wall surface of the boiler furnace is composed of heat exchanger tubes and a multiple of burners to burn the fuels such as pulverized coal, fuel oil, heavy oil, etc. in the furnace are installed on the wall surface of the boiler surface.
FIG. 10 is a schematical drawing to show a boiler, which uses pulverized coal as the fuel.
In the figure, reference numeral 1 denotes a furnace of a coal fired boiler, and pulverized coal burner groups 2 are arranged in a number of stages (3 stages shown in FIG. 10) on a lower portion of the furnace 1. Each of the pulverized coal burner groups 2 has a pulverized coal burner 3 arranged as many as required in horizontal direction along the wall surface.
On an upper portion of the pulverized coal burner groups 2 (downstream side), over air port groups 4 are installed in as many stages as required (one stage shown in the figure). Each of the over air port groups 4 comprises an over air port 5 arranged as many as required in horizontal direction. Each of the over air ports 5 is provided respectively so that it is positioned vertically above each of the pulverized coal burner 3.
To the pulverized coal burner groups 2, a combustion air is supplied via combustion air supply routes 6 and 7. Further, the air for two-stage combustion is supplied to the over air port group 4 via a combustion air route 8 for over air port which branches from the combustion air supply route 6. Pulverized coal is supplied together with the combustion air to the pulverized coal burner 3 from a coal pulverizer (not shown).
Dampers 9 and 10 for adjustment of an airflow rate are installed on the combustion air supply route 7 connected to the pulverized coal burner 3 and on the combustion air route 8 for the over air port connected to the over air port 5.
Next, referring to FIG. 11, description will be given on an example of a conventional type burner in the pulverized coal burner 3.
In FIG. 11, reference numeral 1 denotes a furnace, and numeral 12 represents a furnace wall of the furnace 1.
A throat 13 is provided on the furnace wall 12, and a wind box 14 is mounted on the furnace wall 12 on a side opposite to the furnace 1. Inside the wind box 14, the pulverized coal burner 3 is mounted concentrically to the throat 13. The combustion air supply route 7 is connected to the wind box 14.
The pulverized coal burner 3 is provided with a nozzle main unit 16, and a secondary air regulator 17 designed to surround a forward end (an end at an inner side of the furnace) of the nozzle main unit 16.
The nozzle main unit 16 comprises an outer nozzle 18 and an inner nozzle 19, which are provided concentrically, and an oil burner 20 which is arranged along a centerline of the inner nozzle 19. Cross-sections of each of the outer nozzle 18 and the inner nozzle 19 are designed in circular form. A fuel guiding space 21 is formed between the outer nozzle 18 and the inner nozzle 19. The fuel guiding space 21 is a hollow cylindrical space and its one end is opened.
A primary air intake tube 22 is communicated with a base (an end opposite to the furnace 1) of the outer nozzle 18 from a tangential direction and the primary air intake tube 22 is connected to a coal pulverizer (not shown). The primary air 24 and the pulverized coal carried in the primary air 24 flow into the fuel guiding space 21 from the tangential direction via the primary air intake tube 22 and are spurted out from a forward end of the fuel guiding space 21 while swirling in inner space of the fuel guiding space 21.
At a base of the inner nozzle 19, one end of a tertiary air intake tube 23 is opened, and the other end of the tertiary air intake tube 23 is opened to the wind box 14. The tertiary air intake tube 23 takes the combustion air to be supplied to the wind box 14 and leads the combustion air to the inner nozzle 19 as an auxiliary air for combustion, i.e. as a tertiary combustion air.
The secondary air regulator 17 comprises an auxiliary air regulating mechanism 25 storing the forward end of the nozzle main unit 16 and a main air regulating mechanism 26 provided concentrically and in multiplexed manner on outside of the auxiliary air regulating mechanism 25.
The auxiliary air regulating mechanism 25 has a first air guide duct 28 with its diameter gradually decreased toward a forward end and also has an inner air vane 29 provided rotatably and in multiple number. The inner air vane 29 is synchronically rotatable via a linking mechanism (not shown), and a tilt angle with respect to the air flow can be variable. The main air regulating mechanism 26 has a second air guide duct 32 with its diameter gradually decreased toward a forward end and also has an outer air vane 33 rotatably provided in multiple number at a regular distance in circumference. The outer air vane 33 is synchronically rotatable via a linking mechanism (not shown) in the same way as inner air vane 29, and the tilt angle with respect to the air flow can be variable.
The forward end of the second air guide duct 32 is continuous to the throat 13. The forward end of the first air guide duct 28 is at a position backward from an inner wall surface of the furnace wall 12, and forward ends of the outer nozzle 18 and the inner nozzle 19 are at the positions further backward from the forward end of the first air guide duct 28.
Now, brief description will be given on the combustion of the pulverized coal burner 3. Together with the primary air 24, the pulverized coal is supplied to a base of the fuel guiding space 21 via the primary air intake tube 22. The primary air 24 flows toward the furnace 1 while swirling in the fuel guiding space 21. When the primary air 24 passes through the fuel guiding space 21, the flow of the air is reduced in size, and the primary air 24 is spurted out from the forward end of the outer nozzle 18. To the wind box 14, the secondary air 34, which is air for combustion, is supplied with its temperature at a value as required. A swirling flow is given to the secondary air 34 by the outer air vane 33, and the secondary air 34 is spurted out to the furnace 1 together with the primary air 24 and with the pulverized coal via the second air guide duct 32.
When the pulverized coal is spurted out to the furnace 1, the pulverized coal is homogeneously mixed while being swirled in the fuel guiding space 21. Then, the temperature of the pulverized coal is risen by the secondary air 34 and is further heated up by receiving radiation heat from the furnace 1. By this heating, volatile matter is released from the pulverized coal. Then, the volatile matter is ignited, and flames are continuously maintained.
A part of the secondary air 34 taken into the secondary air guide duct 32 is sent into the first air guide duct 28 via the inner air vane 29, and the secondary air 34 is spurted out as secondary auxiliary air. The inner air vane 29 is tilted with respect to the air flow, and the swirling flow is given to the secondary air thus taken in.
By the adjustment of the airflow rate of the outer air vane 33, by the adjustment of degree of the swirling flow and the airflow rate by the inner air vane 29, a supplying amount and condition of flow of the secondary air 34 are changed, and burning condition of the pulverized coal is adjusted.
A part of the secondary air 34 is guided to the inner nozzle 19 via the tertiary air intake tube 23 as a tertiary air 35, and the part of the secondary air 34 is spurted out from the inner nozzle 19. By the tertiary air 35 being spurted out, the burning condition of the pulverized coal is adjusted. Therefore, through the adjustment of the secondary air 34 and the tertiary air 35 etc., the burning condition of the pulverized coal is set to the best suitable condition.
In the conventional type pulverized coal burner 3 as described above, the outer air vane 33 and the inner air vane 29 are connected by linking mechanisms respectively. Therefore, in order to assemble the outer air vane 33 and the inner air vane 29 without ricketiness and with higher accuracy, higher fabrication accuracy of parts and delicate assembling procedure by a skilled technician are required. For this reason, higher manufacturing cost is needed, and it is difficult to reduce the cost.
Further, it would be unavoidable that ricketiness is increased over time in the linking mechanisms. As a result, tilt angles of the inner air vane 29 and the outer air vane 33 are changed from the tilt angles in an initial stage, and degree of the swirling may vary widely. When the angles of the inner air vane 29 and the outer air vane 33 are varied in order to change the airflow rate and the degree of the swirling flow, there have been problems in that an angle inputted does not accurately correspond to an actual change, or time lag may be caused in the change of angles of the air vanes 29 and 33. This may lead to a situation that it is difficult to perform adequate burning control with high accuracy.